The failure of chronic ulcers to heal represents a major health problem in the United States. To identify the processes leading to impaired healing, the cellular mechanisms involved required for efficient wound closure must be understood. Preliminary data demonstrated that collagenase-1, a matrix metalloproteinase (MMP), is prominently and invariably expressed by basal keratinocytes at the migrating tip of epithelium in both normally healing wounds and chronic ulcers. Collagenase-1-producing keratinocytes are not in contact with a basement membrane but rather migrate over the dermal matrix, which is rich in type I collagen, and express integrins not produced in intact epidermis. Furthermore, collagenase-1 is expressed throughout active re-epithelialization, and once the wound is closed and the basement membrane is restored, production of collagenase-1 turned off. These spatial, in vivo observations have led to the hypothesis that altered cell:matrix interactions regulate collagenase-1 expression by keratinocytes at different stages of repair. Indeed, collagenase-1 is induced in human keratinocytes cultured on native type I collagen, but not by other matrix proteins. This project will address the hypothesis that distinct cell:matrix interactions regulate keratinocyte behavior at different stages of epidermal repair. Contact with dermal collagen is proposed to be a critical signal mediating activation of keratinocytes, characterized by expression of integrins, MMPs, and matrix proteins. In addition, restoration of the basement membrane and/or cell-cell contracts at wound closure is proposed to mediate deactivation of basal keratinocytes and a return to the cellular phenotype of the intact epidermis. In support of the hypothesis, preliminary data demonstrates that collagenase-1 expression is repressed in keratinocytes grown on basement membrane proteins, specifically laminin-1. To address these hypotheses, the following aims are proposed: Define the precise cell- matrix interactions in sustaining expression of collagenase-1 and supporting cell migration during repair. Identify the signals controlling the turn-off of collagenase-1 and cessation of cell migration at the completion of re-epithelialization. Use genetically-defined mice to determine the function of collagenase during normal repair in vivo. Completion of these aims requires the resources of Core B and C, and interactions are proposed with other investigators of this Program.